• Minor document fixes.
• Add #[inline] hints to most of embedded-hal functions.
• pwm: rename get_max_duty_cycle to max_duty_cycle.
• delay: Rename DelayUs to DelayNs
• delay: Add DelayNs::delay_ns()
• delay: Add default impls of delay_ms and delay_us based on delay_ns.
• delay: Make the default impl of delay_ms more efficient, it now does less calls to the underlying delay_ns (previously delay_us).
• spi: Rename Operation::DelayUs to Operation::DelayNs, with nanosecond precision.